The invention relates to a shift device for a transmission, consisting of a shift sleeve, displaceable in the direction of the axis of a transmission shaft, for the driving connection of transmission members, of a shift fork engaging into the shift sleeve, and of, as actuator, an element which is rotatable on a shift shaft arranged transversely to the transmission shaft and which cooperates with a foot part of the shift fork.
It is known from WO 01/59331-A to adopt, as actuator a pinion which meshes with a corresponding toothing on the foot part of the shift fork, the shift shaft being driven by an electric gear motor.
This has some disadvantages: the step-up of this movement transmission is constant, which, as a rule, does not correspond to the profile desired for shifting and to the characteristic of the electric motor; especially not when the shift sleeve has synchronization. There are no stops, and the toothing has no blocking action, that is to say it cannot retain the shift sleeve in the respective position. Both factors, however, are particularly important in the case of an electromotive drive. The motor is, of course, to remain currentless after a completed changeover and is even to be capable of being uncoupled in specific applications, even when changeover took place counter to the ever-acting force of a spring. Furthermore, to simplify the control, the motor is to be capable of being moved up against a stop, in order to manage without position or speed sensors.
In order to remedy this, the object of WO 01/59331-A is to provide a detent disk firmly connected to the rotating element and a detent member engaging into a detent recess. Said detent member holds the rotating element after the uncoupling of the electric motor and ensures that this is possible only after a defined end position is reached. However, this remedy is highly complicated and is also not entirely satisfactory in functional terms. Due to the moments acting on the element and consequently on the detent disk (which emanate, for example, from the synchronization or from chamfers of the teeth in order to secure the sleeve against a stop), friction arises which obstructs or completely prevents the changeover. This may also occur when the two elements to be coupled are in an unfavorable relative position. The other gear in each case then cannot be engaged, and the sleeve remains set in the neutral position, which may lead to hazardous driving situations and therefore should not happen. Moreover, due to the long tolerance chain, positioning is inaccurate.
The object of the invention, therefore, is to propose a simple and reliable control which satisfies all functional requirements, in particular safety requirements.